Reemas,
People do use multiple catalogs. Some people use one for originals and another for derivatives. Some for each calendar year. Some when the sizes reach a threshold. If you look on page 8 under "Cataloging Strategies" in the iView manual, it lists a number of ways to use catalogs
http://downloads.iview-multimedia.com/manuals/MediaPro31_Manual_Eng.pdf. I put my originals and derivatives in the same catalog and will start a new one on a calendar year basis or when it reaches a certain threshold of images yet to be determined. I do recommend trying to keep your catalogs to a minimum for ease of management.
You can easily merge catalogs by importing from the File->Import Items->From Catalog File... menu command.
Dan